(1) Field of the Invention:
The present invention relates to trucks suitably used for tunnel kilns.
(2) Related Art Statement:
As shown by way of example in FIG. 5, in a tunnel kiln which fires ceramic shaped bodies by burners provided at sides in a tunnel kiln (hereinafter referred to as "under firing system"), combustion burners 13-1 and 13-2 are provided opposed to each other at lower portions of kiln walls 12 of the tunnel kiln 11 so that shaped bodies 14 are fired by heating the kiln inside with their combustion streams. That is, the shaped bodies 14 are placed on a truck movable in the kiln via supports 16. The opposed combustion burners 13-1 and 13-2 are ignited and their combustion streams are led to a combustion space 17 defined by the supports 16, whereby the shaped bodies 14 are fired from the underside.
Further, as shown in FIG. 7, combustion burners 13-1 and 13-4 may be arranged at upper and lower portions of kiln walls 12 of the tunnel kiln so that combustion chambers 17 are formed above and under the shaped bodies, and shaped bodies may be plied in two stages by shelf plates 18 and the supports 16, and fired in the kiln. When the shaped bodies are fired by this technique, it is also known that a surrounding gas around the shaped bodies is circulated by combustion streams from the upper and lower opposed burners so that a temperature distribution in the kiln is improved.
As shown sectionally and perspectively in FIGS. 6(a) and (b), respectively, supports 16 having a rectangular section have formerly been used on the above truck 15. Therefore, the combustion streams directly impinge upon the supports 16 having the rectangular section in front of the combustion burners 13-1 and 13-2 when the shaped bodies are being moved in the tunnel kiln 11 by the truck 15. As a result, the combustion streams are blown up along the truck without being burned inside the combustion chamber above the truck, and the combustion stream directly contacts with the shaped bodies. Consequently, the shaped bodies may be melted, or cut, deformed or color-changed due to nonuniform firing shrinkage of the shaped bodies at high temperatures.
On the other hand, the construction which has the upper and lower combustion burners as shown in FIG. 7 possesses a shortcoming in that the circulating effect around the shaped bodies weakens and the temperature distribution becomes nonuniform among the upper and lower portions of the tunnel kilns.